Ablation-resistant resinous compositions



United States Patent 3,177,175 AB A'II N-RESI TANT ESINOUS COMPOSITIONS William T. Barry, Jr., Lafayette Hills, Pa., assignor to General Electric Company, a corporation of New York No Drawing. Filed Dec. 1, 1959,8031. No. 856,609 4 Claims. (Cl. 26033.4)

This invention relates to a resinous material, and particularly concerns a resistant plastic composition which has excellent resistance to ablation even when subjected to extreme conditions of gas 'velocity'and temperature.

Various materials have been formulated and tested for use in high temperature service such as in rocket engines, nose cones and the like. Many such materials have been non-castable and are therefore difficult and expensive to manufacture, particularly in large unconventional shapes such as nose cones andt-he like. The necessity of using high pressure presses and autoclaves with expensive steel molds seriously hinders the development of new sizes and shapes, and makes long production lead times necessary.

Other materials, which are readily castable, have been found to have very poor resistance when exposed to high temperatures and high gas velocities, and even though readily manufactured and formed, such materials are unsatisfactory in service.

Other materials which have been produced and tested have had the drawbacks of high modulus of elasticity, low' elongation, and the tendency to exotherm strongly when cured in thick sections. These drawbacks make the material difiicult to cast on a metal back-up because the resulting product tends to crack when subjected to low temperature cycling. Other drawbacks encountered in the art heretofore, include a tendency to chip when subjected to manufacturing routine.

It is accordingly an object of this invention to provide a castable material which has excellent ablation performance even when subjected to exceedingly high temperatures and gas velocities.

Still another object is to provide a material of this type which is readily castab'le, which does not have an unduly high modulus of elasticity, an unduly low elongation, or an undue tendency to exothenm strongly when cured in thick sections, and which can be cast directly on to a metal substructure.

Still another object is to provide a material of the type just discussed, which has a minimum tendency to chip when subjected to manufacture.

Still another object of this invention is to provide a resin which withstands low temperature cycling without cracking when cast in thick sections on a metal backup or insent. 1

Other objects and advantages of this invention will further become apparent hereinafter.

In accordance with this invention, a novel castable ablation material is formulated of approximately three weight equivalents of a resin known as epoxy novolac which comprises the reaction product of epichlorohydrin with a linear phenol formaldehyde resin, approximately l-3 weight equivalents of an anhydride of an acid selected from the group consisting of adipic, polyadipic, pimelic, polypimelic, suberic, polysuberic, azelaic, polyazelaic, sebacic, maleic, chloromaleic, succinic, methyl succinic, phthalic, endomethylene tetrahydrophthalic, and methyl Nadic, and about /22/2 weight equivalents'of a mono or 3,177,175 Patented Apr. 6, 1965 di alkyl ester or a mixture of mono and di esters of orthophosphoric acid, the alkyl group containing from 1-l2 carbon atoms. 1

The terms weight equivalents and weight equivalent parts as used herein areintended to mean parts by weight which are proportional to the equivalent weight of the compound, as distinguished from its molecular Weight. The equivalent weight is the moleciflar weight divided by the number functional groups per molecule. For each compound, the number 'of functional groups per molecule may be determined readily from the nature of the molecule. For example, epoxy novolac may have three glycidyl groups which contain the reactive epoxy group, and therefore the number of functional groups per molecule (or functionality) would be three. With respect to the anhydride, one acid anhydride reacts with one epoxy group to form a polyester, and if this has one anhydride group its functionality is one.

Epoxy novolac polymer is a resin of the formula not where R is selected from the group consisting of hydrogen and glycidyl. Within the scope of this invention, about 3-10 glycidyl groups are present per molecule, and about- 3-10 phenyl other groups per molecule are present. The integer n, in the formula above, therefore is the range of 1-8. All such resins falling within the scope of the foregoing definition are, for the sake of brevity, hereinafter referred to as epoxy novolac polymer.

The acid anhydrides which are suitable in accordance with this invention are those selected from the group consisting of adipic, polyadipic, pimelic, polypimelic, suberic,

ORE

.polysuberic, azelaic, polyazelaic, sebacic, maleic, chloromaleic, succinic, methyl succinic, phthalic, endomethylene tetrahydrophthalic, and methyl Nadic. Methyl Nadic anhydride is also known as methyl bicyclo [2-2-1heptene- 2, 3-dicarboxylic anhydride isomers.

Referring to the mono or di alkyl ester or mixture of mono and di esters of orthophosphoric acid, the alkyl group is preferably butyl. More specificially, the n-butyl group is preferred.

In addition to the foregoing ingredients, it is optional in accordance with this invention to add a flexibilizer in the form of polypropylene glycol in a molecular weight of approximately 425. This may be present in a quantity, in gram moles of from 0 to about 1, assuming 'th'a't the epoxy novolac is present in an amount of about 3 epoxide gram equivalents. In some cases, no flexibili'zer is needed, as for example when the acid anhydride is a polysebacic anhydride having an average molecular Weight of about 2,000, and a degree of polymerization from about 2-20. Such polysebacic anhydride produces very flexible resins with high elongation but having excellent ablation characteristics, even without the inclusion of a flexibilizer. However, use of the two together gives maximum flexibility. Polyethylene glycol may also be used as a fiexibilizer, but is used in a much lesser amount, preferably about /2 the amount of polypropylene glycol.

The first three compositions specified above were found to fail rather prematurely as distinguished from formulations 5 and 6, which had exceedingly good ablation Likewise, otherglycols in small amounts may be incorporated.

Example 1 resistance. This serves to illustrate the importance of The following table illustrates eleven formulations 5 providing more than'about equivalent of the butyl which were, prepared, and gives the results that were obphosphoricester. .In each of the above examples, the tained thereby. Under the heading Ablation Rates, acid anhydride was methyl 'Nadic anhydride, or methyltwo columns appear, one of which gives the resultswhen bicyclo[2-2- 11heptene-2, 3-dicarboxylic anhydride. the material was subjected to a water stabilized are at 7 Example 2 17,000 F., producing a heat flux .of 2,000 B.t.u. per 10.

The following formulations have excellent ablation characteristics, as compared with the'successfulformulations in Example 1. They diifer in their physical and mechanical characteristics.

square foot per second of energy, and reaching a Mach value' of ,.5-.6 for the rate ofmass flow of the gas. The other co1umn,headed Linde Torch, is a test wherein a torch temperature of 5,200" F. is achieved, with a 1,500

TABLE 2' GlyeidylPhenol Formaldehyde Resin Phosphoric Acid Ester AeidAnhydride.

N0. of Phenyl Average No. or (Epoxide) (Acid) weight a Weight groups per glycidyl groups weight equiv- Type equivalent Type Equivalent molecule per molecule alent parts parts Parts 3.0 3.0 3 ie 1 5. 2 4. 2 3 2 Methyl Nadle- 2 3. 5 3. 3 3 1 Sebacic 3 4. 0 3. 8 3 Suberlm 1% 9. 8 9. 1 3 Methyl Nadlc 2% 3. 4 3. 3 3' 1% Maleic 3 3. 8 3. 7 3 2 Azelaie 3 3. 5 3. 4 3 2 Pimelic 1% 3. 2 3. 2 p 3 p 2 50/50 methyl Nadic/se- 1% bacic. 4. 2 4. l 3 1% 1% 4. 4 4. 3 3 1 2 4. 5 4. 2 3 2 6. 1 5. 8 3 1% 2% 6. 0 5. 8 3 1% 2% 5. 3 5. 0 3 1% 2% 8. 2 7. 6 3 v 2% 1% 6. 4 6. 2' 3 1 3. 2 3. 2 3 1 1 4. 3 4. 0 3 1 Phthalie"; 1 3. 2 3. 2 3 50/50 methyl Nadie/se- 3 7 basic. 3. 2 3. 2 3 3 4. 2 4. 1 3 3 5. 2 5.1 3 V 3 B.t.u. per square footper second heat flux, and reaching a Mach value of 1.6.

TABLE 1 Mono n-butyl Standard diameter Epogy Novolae Ester Phos- Methyl Nadie Flexibilizer cylinder-Ablation Rates Formula- (weight equivphorie Acid Anhydride Polypropylene 7 tion No. alent parts) (weight equiv- (weight equiv G c m.w.

. alent parts) alent parts). 425'(mo1es) Water Arc Linde Toreh' (gram/sec.) (gram/see.)

3 0 3 0 22 .40 3 0 2 0 22 40 3 2 0 210 35 3 2 0 140 09 3 1 2 0 120 06 3 1% 1% M 120' 09 3 2 1 M 120 09 3 2 3 120 12 l 3 1 2 115 07 3 1 2 110 07 3 1 y 2 1 110 12 3 1 3 0 10 06 3 2% 1% 0 11 .13

The ablation rates reported in the above table are for Example 3 a standard /2 inch diameter cylinder, exposed directly to the flame conditions specified above, and specify the number of grams lost per second due to ablation.

The following table illustratesthat a glycol flexibilizer TABLE 3 Glyoidyl Phenol Formaldehyde Resin Phosphoric Acid Ester Acid Anhydride Flexibllizer No. of Phenyl Average No. of Weight Weight Weight (Polypropylene groups per glycidyl groups Equivalent Type Equivalent Type Equivalent glycol except molecule per molecule Parts Parts Parts where noted) (moles) 3.0 .3; 3 Adipic -1 1 5. 2 4. 2 3 2 Methyl Nadic 2 1 3. 4 3. 3 3 1% 3 34 3. 8 3. 7 3 2 3 3. 3. 4 3 2 1% 3. 2 3. 2 3 2 Methyl Nadic 1% 1 '4. 2 4. 1 3 1% Chloromal'e'i' 1% 4. 4 4. 3 3 1 2 4. 5 4. 2 3 2 6.1 5. 8 3 1% 2% 1 Polyethylene glycol.

Example 4 A novolac phenolic resin is prepared by reacting 1 mol. 0

of phenol with 0.75 mol. of aqueous formaldehyde in the p esence of a minera a i A ter t e senwpti ts reaction time, the cook is neutralized and excess Water and unreacted materials are stripped off under heat and vacuum to obtain a low molecular'weight polymer having on the average 3 /2 or more phenol groups per molecule (DP=degree of polymerization-=3 A2). This resin is then dissolved in cphichlorohydrin (5-10 moles per phenol group) and treated with a strong base to obtain the polyglycidyl either with 3 /2 or more glycidyl' groups per polymer molecule and an 'epoxide equilavenoof'1'75r (4) 80 g. of the mono n-butyl ester of phosphoric acid (1 equiv.)

.(5) 5 ml. benzyl dimethylamine It is desirable though not necessary to combine 1 and 2 separately from 3 and 4, all at a temperature of 80 C. When 1 and 2 are combined with 3 and 4 .and 5 is added, a slight exotherm takes places and the temperature rises to 90-95 C. The mix is deaerated under vacuum,

poured into open molds and cured in an oven for 16 hours at 125 C. A clear rigid resin with a room temperature tensile strength of greater than 10,000 psi. and a tensile modulus of 5 X psi. is obtained. Outstanding ablation performance is obtained, as is shown in Table 5 which follows Example 12.

The product was cast into the form of a small rocket nozzle. This nozzle was attached to the plenum chamber of an air stabilized arc. The plasma of the are at a temperature of about 12,000 F. with a heat flux of about 2,000'B.t.u./ ft. sec. was ldth'r'ough the nozzle. The material was found to have exceptional resistance to erosion by this plasma and upon inspection the inside surface was found to be lined with a dense strong cari crea e pql ntepy sne glycol in Example 5 to V 213 g. male or 1 equivalent) while maintaining the other components constant produces a clear semi-rigid resin "having a room temperature tensile strength of 5,000 p'JsLi. and a tensile" modulus of 2.5 X10 p.s.i., again with excellent ablation performance as shown in Table 5.

This material, as well as others, may be completely set and ground up, and then used as filler for itself by mixlog with the ingredients'pfrior' to polymerization. was subsequently formed into a nose cone over a metal This baclcup, using a troweling (pottery-type) technique, with excellent results.

' Example 7 Example 8 Replacement of the 2 equivalents of methyl Nadic anhydride in Example 2 by 2 equivalents of each of the following acid anhydrides lead to resins having ablation performance comparable to Example 5. The anhydrides are maleic, succinic, methyl succinic, 'chloromaleic, phthalic, endomethylene tetrahydrophthalic, polyadipic, polysuberic, polypimelic and polyazelaic. (Results in Table 5.)

Example 9 Replacement of the 2 equivalents of methyl Nadic anhydride in Example 5 by 2 equivalents of each of the following acid anhydrides lead to resins having very poor performance in a high temperature supersonic environment and are to be excluded from the spirit of Table 5).

' Y this invention. They are dodecenyl succinic, tetrapropenyl succinic; tetrahydrophthalic, hexahydrophthalic and a dimethyl, butenyl substituted tetrahydrophthalic.

Thisv exampleis included to illustrate that ,theper formance of the good materials is not general and not predictable in the light of present knowledge.

With respect tothe foregoing Examples 5-9 inclusive,

benzyl dimethylarnine may bereplaced byother tertiary amines which catalyze the reaction of carboxylic. acids and acid anhydrides with epoxy groups or they may be i is placed in the flame.

' from a liquid oxygen-alcohol rocket.

' l. (2) Shrouded Air Arc, wherein exceedingly'hot plasma TABLE 4 CHARACTERISTICS OF TESTING METHODS Temp, Heat Flux,- Mach No.

F. B.t.u./it. /sec.

Water Stabilized Are... 15, 000 2, 000 Sub-Sonia" Right cylinder 0.5 diameter. Shrouded Air Arc 1, 400 -.do Cylinder 0.677 diameter, curved testing surface. Linde Blowpipe F.S.J- 5, 200 1, 500 1.6 Right cylinder 0.5 diameter.

Malta Rocket; 5, 400 1, 200 2.6 Conical: 2.5" base diameter; Hemispherical test surface 0.750 diameter.

Radius of curvature=0.5'.

TABLE RESULTS-*LOSSES OF MATERIAL.

Linde Blow- Malta Shrouded Water Sta pipe F.S.J., Rocket, Air Arc, bilizedArc, Material 3 grams/ inches/10 grams/1O sec; grams/10 sec. Remarks sec. weight sec. length weight loss weight loss 7 loss loss Phenolic Resin %+Nylon 1. 3 0.40 1. 6 1. 0 Two best presently available phenolic Cloth 60%. resin systems. Phenolic Resin 40%+High 0. 70 '0. 15 2. 1 2. 2

Silica Cloth (refrasi1) 60%. Example 2... 0.65 1.2' 1.2 Cons1stently excellent performance ina wide range or high temperature plasmas. Example 3 0. 70 '0. 23 1. 2 1. 1 Example 4.-- 0. 70 1. 1 1, 0 Example 5 0. 70 1.2 Average values for all the anhydridcs mentioned in Example 5. Example 6.. 3. 5 1.3 Average values for anhydrides in Example 6. Blowpipe values of 3.5 and 7 high indicate very poor performance. Example 7 1. 6 1. 6 Example 8 3. 0 1. 6 Example 9 3. 3 2. 3

Although length losses are dissimilar, weight losses are about equal since Phenolic-Refresh has a density of 1.75 g./cc. vs. 1.22

g./cc. tor the resin of Example 3.

left out entirely to slow down the reaction rate. also applies to the other examples. 7

Example 10,

This

Example 11 Replacement of 3 equivalents of Resin I inExample 5 by 3 equivalents of the diglycidyl ether of bis-phenol. ace-tone (functionality of 2) leads to very poor materials having high rates of ablation (see Table 5) Example 12 Replacement of 3 equivalents of Resin I in Example 5 by 3 equivalents of 3,4-epyxy-d-methylcyclohexylmethyl- 3,4-epoxy-6-methylcyclohexane-carboxylate (functionality of 2) leads to materials exhibitingvery poor ablation.

swirl of water. The text specimen is then placed in this plasma.

in the appended claims.

not adversely affect theablative properties of this rnaterial can be added to change-certain'of' its physical properties such as mechanical strength, density, and thermal conductivity. Although this invention has been described with reference tospecific test procedures and method steps, it will beappreciated that the invention is directed to the combinations'of materials in specific proportions as specified in the claims, and is not limited to-methods of preparation orof testing; Moreover, itwill be under stood that this invention embraces equivalents of the compounds that are specifically setforth, all'as appears The, following is claimedz. V I

1. A resinous material consisting essentially by weight of approximately 3 weight equivalent parts of a resin of the formula where R is selected ,fromthegroup consisting of hydrogen and glyoidyLwherein from-3 to 10 glycidyl groups are-present per molecule, andwherein n; represents an integer from 1 to .8, ,aboutl to 3 weight 'equivalents of an anhydride 'of'an acid selected from the group consisting. of adipic, polyadipic, pimelic, polypimelic, subei'ic,

polysuberic, azelaic, polyazelaic, subacic, maleic, chloronialeic, succinic, methyl succinic, phthalic, endomethyltene-2,3-'dicarboxylic acids and about /2 to 2 /2 weight equivalents of a material selected from thevgroup consisting of mono and dialkyl ester of orthophosphoric acid, said alkyl group containing from 1 to 12 carton atoms, said weight equivalents being equal to the molecular weight of'th'e constituent composition divided by the number of functional groups per molecule.

2. A low pressure moldable ablation material consisting essentially by weight of approximately 3 weight equivalents of a resin of the formula wherein R is selected from the group consisting of hydrogen and glycidyl, wherein from 3 to glycidyl groups are present per molecule, and wherein n represents an integer from 1 to 8, about 1 to 3 Weight equivalents of methylbicyclo [2 2 1 heptene-2,3-dicarboxylic anhydride isomer, and about /2 to 2 /2 weight equivalents of a material selected from the group consisting of mono and dialkyl ester of orthophosphoric acid, said alkyl group containing from 1 to 12 carbon atoms, said weight equiv- V alents being equal to the molecular weight of the conheptene-2,3-dicarboxylic anhydride isomer, said weight equivalents being equal to the molecular weight of the constituent composition divided by the number of functional groups per molecule.

4. A resinous material consisting essentially by weight 1 0 of approximately 3 weight equivalent parts of a resin of the formula OR 3R (|)R H, 9 El 11 MD- where R is selected from the group consisting of hydrogen and glycidyl, wherein from 3 to 10 glycidyl groups are present per molecule, and wherein n represents an integer from '1 to 8, about 1 to 3 weight equivalents of an anhydride of an acid selected from the group consisting of adipic, polyadipic, pimelic, polypimelic, suberic, polysuberic, azelaic, polyazelaic, subacic, maleic, chloromaleic, succinic, methyl succinic, phthalic, endomethylene tetrahydrophthalic, and methylbicyclo[2- 2- 11hepteno2, 3-dicarboxylic acid, about /2 to 2 /2 weight equivalents of a material selected from the group consisting of mono and dialkyl ester of orthophosphoric acid, said alkyl group containing from 1 to 12 carbon atoms, and for the purpose of imparting flexibility about 4 to 1 mole of a glycol selected from the group consisting of polypropylene glycol, polyethylene glycol, 1,3 propane diol, 2,2 dimethylpropane diol, 2,2 diethyl propane diol, 1,4 butane diol, 1,5 pentane diol, 1,6 hexane diol of molecular weights ranging from monomer to about 2,000, said weight equivalents being equal to the molecular weight of the constituent composition divided by the number of functional groups per molecule.

References Cited by the Examiner UNITED STATES PATENTS 2,587,477 2/52 Hunter 26045.7 2,609,351 9/52 Taat 26059 2,716,099 8/55 Bradley 26047 2,849,418 8/58 Fang 26047 2,863,853 12/58 Pschorr 26047 2,897,175 7/59 Howe et a1 26059 3,063,965 11/62 Cololough 26059 3,127,373 3/64 Guttag 26059 OTHER REFERENCES Lee et al.: Epoxy Resins, pages 5l-52, McGraw-Hill Book Co. (1957).

WILLIAM H. SHORT, Primary Examiner.

R. L. CAMPBELL, L. D. ROSDOL, Examiners. 

4. A RESINOUS MATERIAL CONSISTING ESSENTIALLY BY WEIGHT OF APPROXIMATELY 3 WEIGHT EQUIVALENT PARTS OF A RESIN OF THE FORMULA 